CENOZOIC ORGANIC MOLECULAR ISOSCAPES: PLANT WAX HYDROGEN ISOTOPE RECORDS OF CHANGING PRECIPITATION ISOTOPES AND CLIMATE ACROSS NORTH AMERICA

Warm Cenozoic climate states provide a model for understanding latitudinal climate gradients and regional hydrologic variability in a warm, high CO₂ world. Over past decades, there has been considerable work constraining large-scale isotope hydrology and climatic variability on the continental scale. Reconstructed paleoprecipitation isotopes can aid in constraining tectonic and climatic change over long timescales. Organic molecular proxies provide a relatively new tool for understanding isotopes of paleoprecipitation that can be related to these climatic and tectonic factors. This talk will present hydrogen isotope data from higher plant waxes preserved in Eocene through Miocene-aged sedimentary basins across western North America to evaluate large-scale spatial patterns of isotope hydrology and climate during Cenozoic warm periods. These data are coupled with modern regional biomarker C and H isotope data and event specific (Middle Eocene Climatic Optimum (MECO) and Middle Miocene Climatic Optimum (MMCO)) biomarker isotope records to assess temporal changes in isotope hydrology and climate during Cenozoic warm periods. Regional and event-specific terrestrial wax data show generally wetter and warmer conditions than today in western North America, with reduced latitudinal gradients in paleoprecipitation isotopes during the Eocene, and a transition to near modern patterns in the Miocene. Records of short-duration, CO₂-driven events (e.g. MECO, MMCO) show changes to regional hydrology in concert with atmospheric perturbations to pCO₂ during warming events. These new Cenozoic organic molecular isoscapes can help to provide new constraints on the long-term evolution of the North American Cordillera as well as changing climate and hydrology over long timescales.